1. Field of Invention
The present invention relates to a microcrystalline alloy, a method for the production of the alloy, an apparatus for the production of the alloy, and a method for the production of a casting of the alloy. The present invention is directed, in particular, to an Al—Si alloy.
2. Description of Related Art
It is widely known that when a liquid is irradiated with ultrasonic waves, an acoustic stream or ultrasonic cavitation is generated in the liquid. Many applications of ultrasonic waves to metal liquid-phase processes have also been reported, and, above all, refinement of a solidification structure by ultrasonic waves has been conventionally known. It is also said that a physical phenomenon such as ultrasonic cavitation closely relates to refinement of metal crystal grains, and applying ultrasonic vibration to a casting process has become common knowledge.
For example, Japanese Patent Application Publication No. 7-278692 (JP-A-7-278692) describes a method for the production of a hypereutectic Al alloy die-cast member that has an Si content of 20 to 40%. The production method achieves refinement of coarse acicular primary crystal Si by immersing an ultrasonic vibrator into a melt of a material and applying ultrasonic vibration to the melt through the ultrasonic vibrator to produce a die cast member that has high strength.
Japanese Patent Application Publication No. 2006-102807 (JP-A-2006-102807) describes a method for reforming a metal structure. In this method, ultrasonic vibration is applied to a molten metal in a mold from a horn located a specified distance away from the surface of the molten metal. Then, fine nuclei are formed in the molten metal and dendrites of the primary crystal are destroyed, resulting in a fine solidification structure.
Japanese Patent Application Publication No. 7-90459 (JP-A-7-90459) describes an abrasion-resistant aluminum alloy and a method for the production of the alloy. The machinability and hot workability of the alloy are improved by reducing the Si content to a value that is lower than those of conventional aluminum alloys and adding P instead, and by properly setting the contents of Mn, Ni, Cr, and Zr.
However, only the refinement of the primary crystal Si can be achieved by the technique that is described in JP-A-7-278692, and the refinement of primary crystal α-Al cannot be achieved by the technique. In addition, since the ultrasonic vibrator is immersed into the melt, the ultrasonic vibrator is deteriorated by adhesion of the melt.
Also, with the technique that is described in JP-A-2006-102807, microcrystalline grains cannot be refined while macrocrystalline grains can be refined.
Further, the technique that is described in JP-A-7-90459 is a method for refining the primary crystal Si by applying chemical means such as additives, and it is expected that various components that are added as additives cause various problems such as poor recyclability, increase in workload for preparation and control of the additives, segregation during casting, chipping during machining, and corrosion and diffusion during use. In addition, addition of such additives can achieve the refinement of the primary crystal Si but cannot achieve the refinement of the primary crystal α-Al.
In other words, with the above crystal refinement techniques that employ an ultrasonic vibration method, only the refinement of macrocrystalline grains can be achieved, and it is difficult to achieve the refinement of a microcrystalline structure. Specifically, in order to achieve the refinement of the microcrystalline structure, a technique is required by which the primary crystal α-Al can be crystallized.